The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
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Wegovy Weight Loss Injection — How It Compares to Mounjaro
Wegovy is a prescription-only weekly weight loss injection licensed in the UK that contains semaglutide. It works by activating GLP-1 receptors to reduce appetite and help you feel fuller faster. Many people wonder how Wegovy compares to Mounjaro, another popular weekly weight loss injection. While both are effective options, they work differently and have distinct dosing schedules. Understanding the differences helps you and your GP or prescriber decide which might be more suitable for your individual circumstances.
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Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
How Wegovy and Mounjaro Differ
Mechanism of action: Wegovy contains semaglutide and works as a GLP-1 receptor agonist only, activating one hormone pathway to regulate appetite and blood sugar. Mounjaro contains tirzepatide and is a dual GIP and GLP-1 agonist, activating two pathways, which some research suggests may produce slightly different effects.
Dosing and escalation: Wegovy starts at 0.25 mg and escalates weekly from 0.5 mg, 1 mg, 1.7 mg to a maximum of 2.4 mg over approximately 16 weeks. Mounjaro starts at 2.5 mg and escalates every 4 weeks to a maximum of 15 mg, meaning fewer dose steps overall.
Clinical trial results: In the STEP-1 trial, Wegovy showed average weight loss of approximately 15% of body weight. Mounjaro's SURMOUNT-1 trial showed average weight loss of 15–21%, though individual results vary significantly with both medications.
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How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Which Is Right for You?
Neither Wegovy nor Mounjaro is universally "better"—both are prescription-only medications that require clinical assessment and must be prescribed by a licensed healthcare professional or prescriber. Eligibility depends on your BMI, health conditions, medical history, and current medications. Use our free GLP-1 weight loss calculator to explore potential weight loss outcomes at different doses. Your GP or specialist can assess which medication may be more appropriate based on your individual circumstances, including any contraindications or interactions with other medications you take. Both work best alongside reduced-calorie diet and increased physical activity.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
Is Wegovy a weekly injection?
Yes. Wegovy is administered as a once-weekly injection using a pre-filled pen. Each pen contains enough for 4 weeks of injections. You can inject it into your stomach, thigh, or upper arm, and sites should be rotated weekly.
What are the main side effects of Wegovy?
Very common side effects include nausea, diarrhoea, vomiting, and constipation—especially during dose escalation. Most side effects decrease over time. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and severe allergic reactions, which require immediate medical attention.
How long does Wegovy stay in your system?
Semaglutide is gradually eliminated from your body. After stopping Wegovy, appetite-suppressing effects typically begin to diminish within a few days, though some people notice gradual increases in hunger and appetite over 2–3 weeks as the medication leaves their system.
Can I get Wegovy on the NHS in the UK?
NICE has approved semaglutide for weight management, but NHS availability is limited to specialist tier 3 or 4 weight management services. Access varies significantly by region, and waiting lists can be very long. Many people access Wegovy privately through online prescribing services following clinical assessment.
What's the difference between Wegovy and Ozempic?
Both contain semaglutide, but Ozempic is licensed for type 2 diabetes (up to 2 mg) while Wegovy is specifically licensed for weight management (up to 2.4 mg). Ozempic is not licensed for weight loss in the UK, though off-label use is sometimes discussed in clinical settings.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.